Microstructural and texture changes during equal channel angular pressing of an Al–Mg–Sc alloy

Abstract

Evolution of the microstructure and microtexture of an Al–Mg–Sc alloy during equal channel angular pressing (ECAP) at 200 °C was studied. Increasing the ECAP strain of 1 < ε < 4 was accompanied by a rapid hardening followed by a saturation of microhardness at the higher strains. Straining to ε ≤ 4 did not result in any significant structural changes on a mesoscopic level: e.g. the original grains were mainly rotated toward the shearing direction in accordance with the simple shear deformation mode. At that, the texture changes were characterized by creation of a relatively strong duplex texture, typical for conventional high-strain axi-symmetric deformation of fcc metals, i.e. the directions of <100> and <111> were oriented parallel to the pressing direction (PD). At ECAP strains larger than 4, in contrast, significant changes took place in both the microstructure and the texture evolved. Those were mainly related to the frequent formation of microshear bands developed in various directions, that resulted in the local lattice rotations toward <110> and frequent nucleation of new ultrafine grains at high strains. Ultrafine crystallite structures were formed in the alloy characterized by the fraction of high-angle boundaries of about 40–45% and a texture with the near <110> maximum oriented in PD at the highest strain of ε = 12.